Bridge Structures         
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There are three major types of bridges:

  • the Beam bridge

  • the Arch bridge

  • the Suspension bridge

The biggest difference between them is the maximum length of a single span. 
(A span is the distance between two bridge supports.)

  • A beam bridge can span up to 200 feet, 

  • A modern arch can span up to 800 or 1,000 feet.

  • A suspension bridge can span up to 7,000 feet.

What allows a bridge to span greater distances ?
The answer is found by explaining two important forces called Compression and Tension:

  • Compression is a force which squashes the stone, brick, or steel.

  • Tension is a force which acts to stretch the material.

It's the job of the bridge design to prevent compression and tension
 forces from twisting (buckling) or snapping parts of the bridge.

 The best way to deal with these forces is to
spread them out ( dissipate them)  e.g. Arch Bridge
or pass them on ( transfer them)  e.g. Suspension Bridge

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